1. Field of the Invention
The present invention relates to an optical pickup apparatus, an integrated circuit, and a method for controlling laser output of an optical pickup apparatus.
2. Description of the Related Art
An optical pickup apparatus, configured to perform recording and reproducing signals for an optical disc, detects a laser beam emitted from a laser diode with a photodetector such as a photodiode, thereby controlling the output of the laser diode according to the intensity of the detected laser beam.
For example, Japanese Laid-Open Patent Publication No. 2003-132581 discloses, in FIG. 5, a back monitor type optical pickup apparatus configured to detect a laser beam emitted backward (which is not a direction of an optical disc) from a laser diode with a photodetector (back monitor photodetector) provided within the same package as that provided with the laser diode thereby controlling the drive current of the laser diode. For example, Japanese Laid-Open Patent Publication No. 2003-132581discloses, in FIG. 4, a front monitor type optical pickup apparatus configured to detect a laser beam emitted forward (which is a direction of an optical disc) from a laser diode with a photodetector (front monitor photodetector) other than the back monitor photodetector thereby controlling the drive current of the laser diode.
FIGS. 3 and 4 respectively depict examples of configurations of typical laser output control circuits in the back monitor type optical pickup apparatus and the front monitor type optical pickup apparatus.
As depicted in FIG. 3, a back monitor photodiode (photodetector) PD1 receives a laser beam emitted backward from a laser diode LD1, and a current Ibm according to the intensity of the received laser beam flows through the photodiode PD1. Further, the current Ibm flows through a variable resistor VR adjusted depending on an optical disc, and a voltage Vbm generated across the variable resistor VR is converted into a digital signal by an ADC (analog-digital converter: analog-digital converter circuit) 12, and then inputted to an LD drive circuit 13. The LD drive circuit 13 controls a drive current Ild1 supplied from a power source 14 according to the voltage Vbm thereby controlling the output of the laser diode LD1.
Whereas, as depicted in FIG. 4, a front monitor photodiode PDfm receives a laser beam emitted forward from a laser diode LD2, and a current Ifm according to the intensity of the received laser beam flows through the photodiode PDfm. Further, the current Ifm is converted into a voltage signal Vfm by an IV amplifier (current/voltage converter circuit) 44, further converted into a digital signal by an ADC 22, and then inputted to an LD drive circuit 23. The LD drive circuit 23 controls a drive current Ild2 supplied from a power source 24 according to the voltage Vfm thereby controlling the output of the laser diode LD2. The IV amplifier 44 includes a plurality of resistors for selecting a gain and a switch circuit (not depicted) configured to switch a resistor to be connected, and the gain can be adjusted by inputting a selection signal SEL in accordance with an optical disc from a controller 50.
As such, the laser beam emitted from the laser diode is detected by the back monitor photodetector or the front monitor photodetector, thereby being able to control the output of the laser diode.
In the back monitor type laser output control circuit depicted in FIG. 3, the current Ibm, flowing through the photodiode PD1 provided within the same package as that provided with the laser diode LD1, is converted into the voltage Vbm using the variable resistor VR, to be used as a monitor signal indicative of the intensity of the laser beam. Therefore, the back monitor type enables inexpensive configuration of the laser output control circuit, and is mainly employed in an optical pickup apparatus configured to perform only reproducing operation.
On the other hand, in the front monitor type laser output control circuit depicted in FIG. 4, the current Ibm, flowing through the photodiode PDfm other than the photodiode PD2, is converted into the voltage Vfm using the IV amplifier 44, to be used as a monitor signal. The front monitor type enables faster response than that in the case of the back monitor type, and is therefore mainly employed in an optical pickup apparatus performs not only reproducing operation but also recording operation that requires high-speed control of the output of the laser diode.
By way of example, in an optical pickup apparatus that performs both recording and reproduction for CD (compact disc) and DVD (digital versatile disc) and performs only reproduction for BD (Blu-ray disc), a laser output control circuit for CD/DVD can be of the front monitor type and a laser output control circuit for BD can be of the back monitor type.
However, in the case of reproduction of a multilayer (two or more layer) BD, the output of the laser diode is required to be about 10 times greater than that in the case of reproduction of a single-layer BD. Therefore, in order to support reproduction of multilayer BD, the laser output control circuit depicted in FIG. 3 is required to use two variable resistors and adjust them depending on single-layer and multilayer BDs, respectively, and it is also required to further add a switch circuit that switches the two variable resistors.